Air filters are commonly used in forced air systems (e.g., residential heating and air-conditioning systems) in order to remove dust and dirt particles and the like. Air filter products typically include a filtration media surrounded and supported by a frame. Additional supporting components, such as a mesh screen, adhesive beads, etc., may also be included. However, the frame is not only sized and shaped to partially enclose and support the filtration media, but also sized and shaped so that the air filter product can be inserted or supported in place based upon a particular end-use application. As a point of reference, the three-dimensional shape of an air filter product includes a length, width, and depth. In the case of a rectangular air filter product, for example, a rectangular filtration media is surrounded at its four sides by frame pieces or segments that may be connected at the corners and/or connected to the four side edges of the filtration media. The majority of the filtration media is thus capable of use for its filtering ability, with air flow through the filtration media occurring in the depth direction. Many end-use applications have a filter-receiving housing with established length, width, and depth dimensions; the air filter product's outer dimensions desirably match one or more of the expected housing length, width and/or depth dimensions to achieve robust retention of the air filter product upon insertion into the housing.
Air filter frame elements are known to be made from a variety of materials, including metal, plastic, and paperboard. In many instances, a selected construction of the air filter frame is a function of the filtration media format. For example, the filtration media can be formed to a pleated or other three-dimensional shape. The frames associated with these filtration media formats must accommodate the elevated, overall three-dimensional depth. In other instances, the filtration media can be relatively flat or planar (e.g., non-pleated). In theory, the frame could also have a relatively minimal depth (corresponding with that of the flat filtration media format); however, in order to facilitate robust retention within the expected end-use filter-receiving housing, the frame will oftentimes define an elevated depth (as compared to a thickness or depth of the flat filtration media), including side panels or walls projecting well away from a major surface of the filtration media to define an overall depth of the air filter product that corresponds with the depth of the end-use filter-receiving housing.
The projecting frame format associated with many flat filtration media-based air filter products has been found to present a unique opportunity for reduced shipping costs. In particular, the depth-defining side panels or walls can be formed to extend at a non-perpendicular angle relative to the plane of the flat filtration media. With this design, a first air filter product can nest “inside” the frame of a second air filter product when stacked on top of the other. This nested or stacked arrangement significantly reduces the resultant shipping volume, and thus shipping costs, when the air filter products are delivered in bulk. These same nested arrangements, and thus shipping cost savings, can also be accomplished with other air filter product designs, including pleated filtration media-based products having projecting frame walls or panels establishing the air filter product's overall depth.
One example of a nesting frame construction for a flat filtration media air filter product is provided in U.S. Publication No. 2013/0327004, entitled “Framed Air Filter with Offset Slot, and Method of Making,” the entire teachings of which are incorporated herein. The frame design of the '004 Publication is a strip-frame, which means that individual frame pieces are cut as linear strips for a continuous roll of frame material (e.g., chipboard) with very little waste. Four distinct or discrete strips are used to complete a rectangular air filter product. The nested strip frame design of the '004 Publication, while excellent in reducing shipping costs, may come with a penalty in manufacturing productivity due to the need to assemble four strip pieces.
Standard strip frames for non-nesting filters often have a hinged corner joint, which allows for rapid assembly in manufacturing because the hinge design reduces the number of frame pieces from four to two or even one. However, the hinged frame is not designed to provide filter-to-filter nesting such that the shipping and cost savings described above are not available.
Single piece nestable frames for flat filtration media air filter products are known, for example fiberglass-based residential air filter products available from Flanders Corp. However, these known frames are die-cut from a single piece of chipboard in a “box frame style” configuration and are accordingly much more expensive than a perimeter-only strip frame.